Adding mask formatting example (#287)

examples/mask.js

@@ -0,0 +1,62 @@
+const { format } = require('../');
+
+const apiResponse = {
+  creditCard: 1111222233334444,
+  ssn: 4873945739834,
+  customer: {
+    firstName: 'Jim',
+    lastName: 'Davis',
+    address: {
+      number: '404',
+      street: 'Poughkeepsie Lane',
+      city: 'Alpharetta',
+      state: 'GA'
+    }
+  },
+  accounts: [
+    {
+      bank: 'Bank of America',
+      accountNumber: 1290382430
+    },
+    {
+      bank: 'Chase',
+      accountNumber: 423523235
+    },
+    {
+      bank: 'Wells Fargo',
+      accountNumber: 1554235555235460
+    }
+  ]
+};
+
+const maskDataFormat = format((info) => {
+  const mask = (data, maskCharactersVisible = 0, maskCharacter = '*') => {
+    Object.keys(data).forEach((key) => {
+      const strKey = `${data[key]}`;
+      const strLength = strKey.length;
+      if ((typeof data[key] === 'object' || Array.isArray(key)) && data[key]) {
+        mask(data[key], maskCharactersVisible, maskCharacter);
+      } else if (key === 'accountNumber' || key === 'creditCard') {
+        if (maskCharactersVisible > 0 && maskCharactersVisible < strLength) {
+          data[key] =
+                  maskCharacter.repeat(
+                    strKey.slice(0, strLength - maskCharactersVisible).length
+                  ) + strKey.slice(strLength - maskCharactersVisible);
+        } else {
+          data[key] = maskCharacter.repeat(strLength);
+        }
+      }
+    });
+
+    return data;
+  };
+
+  mask(info.message, 4, '%');
+  return info;
+});
+const mdf = maskDataFormat();
+
+console.dir(mdf.transform({
+  level: 'info',
+  message: apiResponse
+}));